In recent years, the industry of medical diagnostic film and photographic plate-making film has been in great need of reduction of amount of waste liquid from processing from the standpoint of environmental protection and space saving. This has made it necessary to develop a technique for heat-developable photosensitive material as a medical diagnostic film and photographic plate-making film which can be efficiently exposed using a laser image setter or laser imager to form a clear black image having a high resolution and sharpness. The use of such a heat-developable photosensitive material makes it possible to eliminate the necessity of solution-based processing chemicals and hence provide customers with a simpler heat-development system that doesn't damage environment.
Although the art of ordinary image-forming materials has similar requirements, in particular, medical diagnostic images must be finely drawn and hence need a high quality such as high sharpness and graininess. Further, images having cold black tone are desirable from the standpoint of ease of diagnosis. At present, various hard copy systems utilizing pigment and dye such as ink jet printer and electrophotography have been on the market as ordinary image forming systems. However, none of these image forming systems are satisfactory as medical image outputting systems.
On the other hand, a heat image forming system using an organic silver salt is disclosed in U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. Klosterboer, “Thermally Processed Silver Systems”, Imaging Processes and Materials, Neblette, 8th edition, compiled by J. Sturge, V. Walworth, and A. Shepp, Chapter 9, page 279 (1989).
In particular, a heat-developable photosensitive material normally comprises a photosensitive layer having a catalytically active amount of a photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., organic silver salt) and optionally a toning agent for controlling the tone of silver dispersed in a binder matrix.
The heat-developable photosensitive material which has been imagewise exposed to light is then heated to a high temperature (e.g., 80° C. or higher) so that the reducible silver salt (which acts as an oxidizing agent) undergoes redox reaction with the reducing agent to form a black silver image. The redox reaction is accelerated by the catalytic action of the latent image of silver halide produced by exposure. Therefore, the black silver image is formed on the exposed area. For the details of this mechanism, reference can be made to many literatures, including U.S. Pat. No. 2,910,377 and JP-B-43-4924 (the term “JP-B” as used here in means an “examined Japanese patent publication”).
It has been keenly desired to further develop the aforementioned environmentally friendly heat-developable photosensitive material having an excellent handleability, preservability and image preservability after heat development and a wrapping material and a wrapping method therefor.
A heat-developable photosensitive material comprising an organic silver salt undergoes no fixing of organic silver salt and other materials and thus can likely have a silver image to appear when acted upon light or heat even after the formation of silver image by heat. It is a matter of course that such a trouble does not occur under ordinary working conditions. However, when the film processed is stored under very severe conditions for heat-developable photosensitive material, e.g., when the film is kept in a car in summer season for transporting purpose or like purposes, the film undergoes troubles such as entire discoloration and transfer of letters on the bag in which the film is wrapped to the film, i.e., fog.
When the heat-developable photosensitive material is subjected to development after stored in the form of wrapped sheet film, it can undergo density change under the influence of the wrapping material.
In order to inhibit the change with time during the storage in the form of wrapped film, a wrapping material comprising a polypropylene or polyethylene sheet has been proposed. These synthetic resin sheets are disadvantageous in that they have so high a chargeability as to attract dust in the air, which adhere on the heat-developable photosensitive material, thereby causing white spot (WS). A wrapping material comprising an aluminum foil laminated thereon has been proposed as another wrapping material. However, this wrapping material cannot be recycled as used paper. Further, even when combusted, this wrapping material leaves the aluminum foil incompletely combusted. This aluminum foil is then accumulated in the incinerator. Accordingly, this wrapping material is undesirable from the standpoint of environmental protection.